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Playing the piano. This activity is an example of human dexterity impossible for a robot to reproduce accurately. The rapid smooth changes in length and tension of the muscles require a very complex feedback mechanism. Receptors within the muscles detect the length, tension, and changing length. This information is used by the brain to modify further movements allowing damped, finely controlled activity. Practice, that is, repetition of the same movements, allows the brain to learn the muscle and joint actions, and less correction is necessary. Speed and accuracy increase as the skill is learned in this way.